An image sensor is a device which converts an optical image into an electrical signal. The image sensor is used in a digital camera or other image processing devices. The image sensor includes a plurality of pixels.
In general, a mechanical shutter method or an electrical shutter method is used to control an exposure time that determines the amount of photocharges on which the electrical signal is based.
First, in the mechanical shutter method, light to be incident on the plurality of pixels is physically blocked by using a mechanical device.
Second, the electrical shutter method is employed mainly in a complementary metal-oxide semiconductor (CMOS) image sensor (hereinafter referred to as a CIS). In the electrical shutter method, an integration time during which the photocharges are generated and accumulated is electrically controlled.
Examples of the electrical shutter method include a rolling shutter method and a global shutter method.
In the rolling shutter method, the integration time is controlled to be different in units of rows of a pixel array. In the global shutter method, the integration time is controlled to be the same with respect to all the rows of the pixel array.
A light-emitting diode (LED) light has been widely used in a traffic light, a speed-limit sign, etc. The LED light has a specific low-frequency component. That is, in the case of the LED light, an ‘on’ period (a period in which an LED is ‘on’) and an ‘off’ period (a period in which the LED is ‘off’) are alternately repeated at specific intervals of time, thereby causing flickering to occur.